This invention relates to molding plastic articles which have internal threads. More particularly, it relates to ejecting the articles from the mold core.
When molding internally threaded articles, such as a screw-on lid for a container, the mold core is provided with the depressions which form the resulting internal threads of the article. The resulting mating of the article threads with the core depressions creates a barrier to axial ejection of the article. Before the article may be ejected the core must be disengaged from the article. Various techniques have been employed for removing these articles from their molds. One such technique is to unscrew the core from the article. This technique requires that the article be held immobile so that when the core is rotated, the article does not rotate with it. This has previously been accomplished by the provision of additional molded members on the article for engagement with, for example, the cavity-half of the mold. Once the core is unscrewed from the article, a further step is required to remove the article from the mold. Another drawback of this procedure has been the large amount of wear between rotating core members and non-rotating members.